AN1372 - Digital HID Ballast Reference Design

AN1372
Automotive Headlamp HID Ballast Reference Design
Using the dsPIC® DSC Device
Author:
Jin Wang
Microchip Technology Inc.
INTRODUCTION
In recent years, High Intensity Discharge (HID) lamps
have been accepted as a good lighting source for
automotive headlight applications. However, the startup process of an automotive HID lamp is complex. It
consists of six stages and each stage presents different
characteristics, which need different control strategies.
Compared with conventional halogen lamps, Xenon
lamps have features of high luminous efficacy, low
power consumption, good color rendering and long
lamp life. Xenon lamp automotive headlamp systems
greatly improve the safety of driving at night.
FIGURE 1:
VOLTAGE AND CURRENT
OF HID LAMPS AT STEADY
STATE
V
A digitally controlled ballast has many advantages over
the traditional analog approach:
• Convenient implementation of sophisticated
control algorithms
• High performance operation
• Effective protection
• Very robust
• Low cost
This application note focuses on the implementation of
an automotive HID electronic ballast using a Microchip
GS-series 16-bit Digital Signal Controller (DSC).
HID Lamp
Gas is a good insulator under normal conditions.
However, special conditions such as a strong electric
field, x-ray radiation, ion bombardment, and high
temperature heat could lead to ionization of gas
molecules and produce free-charged particles. These
charged particles can conduct current under an electric
field, which is known as gas discharge.
The light source made by this principle is called a gas
discharge lamp. A HID lamp is one kind of gas
discharge lamp. Others include high-pressure mercury
lamps, high-pressure sodium lamps, metal halide
lamps and some rare gas lamps, such as Xenon and
Krypton lamps.
HID lamps have many advantages over incandescent
and fluorescent lighting, such as long lamp life, high
efficiency, high brightness and low power consumption.
They are widely used in factory buildings, airports,
stadiums and square-shaped lighting fixtures. In
addition, Xenon lamps are widely used in automotive
applications.
© 2011-2012 Microchip Technology Inc.
I
HID Electronic Ballast
HID lamps present a negative resistance characteristic,
which is shown in Equation 1.
EQUATION 1:
NEGATIVE RESISTANCE
CHARACTERISTIC
dV lamp
----------------- < 0
dI lamp
This means the ballast is unstable if the lamp was
directly connected to a voltage source. A series
positive impedance is needed to ensure the ballast has
a positive resistance characteristic, as shown in
Equation 2. This is the basic ballast principle.
EQUATION 2:
POSITIVE RESISTANCE
CHARACTERISTIC
dV system
--------------------- > 0
dI system
DS01372B-page 1
AN1372
A traditional inductive ballast shown in Figure 2 has
many problems such as large bulk capacitors, low
Power Factor (PF) and difficulty reigniting. An
electronic ballast is used to control the lamp current
and lamp output power. Instant start-up, small size,
high PF, and high efficiency can be achieved using an
electronic ballast.
FIGURE 2:
INDUCTIVE BALLAST
L
AC IN
Good electronic ballasts must have the following
important features:
• High power factor, greater than 0.9 at the ballast
input
• THD should be limited below 33%
• No flicker during the lamp start-up process
• High power efficiency
• No acoustic resonance
Technical Background of Automotive HID
Ballast
The start-up process of automotive HID lamps is quite
complex. Figure 3 shows the working profile of HID
lamp voltage and current during the start-up process.
This is the inherent characteristic of an HID lamp and
the ballast must be designed to meet this profile;
otherwise, the HID lamp will not operate as expected.
Lamp
C
AUTOMOTIVE HID LAMP VOLTAGE AND CURRENT(1)
FIGURE 3:
on
rnTu
30 ms
itio
Ign
n
r
ve
eo
k
Ta
-up
rm
a
W
50 ms
Vlamp(2)
e
tat
y-s
d
a
Ste
p
n-u
Ru
6s-8s
65V-105V
20V-65V
20V-40V
-400V
25 kV
2.5A(max)
Ilamp
2.5A~0.41A
0.41A (@85V,35W)
0A
-12A
max
Note
1:
2:
-2.5A (max)
The data presented in this figure depends on the lamp part number and working conditions.
Vlamp in the turn-on stage is high-frequency AC; in this instance only its profile is illustrated.
• Turn-on: Before ignition, the lamp’s equivalent impedance is
considered as infinite, so the ballast is treated as an open circuit. In
this stage, the ballast produces adequate voltage. In this stage, the
voltage generated by the ballast is fed to the igniter circuitry to ignite
the lamp.
• Ignition: Automotive HID lamps are high pressure gas lamps. During
this stage, the igniter circuitry generates a high voltage pulse across
the lamp and the lamp transfers from isolation status to current
conductive status. As the result, an arc is established in the tube and
visible light is generated. The required ignition voltage for a hot lamp
is around 25 kV. For a cold lamp, the voltage is around 10 kV.
• Takeover: After successful ignition, the lamp requires a large
current (takeover current) to sustain the arc. The output
capacitance and auxiliary current circuit can provide this high
magnitude current before the DC/DC converter delivers enough
power to the lamp.
DS01372B-page 2
• Warm-up: In this stage, the DC/DC converter provides a
certain amount of current, depending on the lamp condition to
sustain the arc. The converter works as current mode, and
generates a square wave AC current. As the frequency is small
(20 Hz) when compared to steady-state, it’s also called DC
status.
• Run-up: This is the key stage of the start-up process. In order
to meet the SAE J2009 and ECE Reg. No 99 specification for
the light output versus time, the start transient power of the
lamp is much higher than the steady state. Then, the ballast
controls the lamp power to ramp down to the normal level.
• Steady State: The lamp voltage is ~ 85V, and the lamp current
is ~0.4A, depending on lamp conditions. But the lamp power is
recommended to be 35W, ±1W. This helps to ensure better
output light performance and longer lamp life.
© 2011-2012 Microchip Technology Inc.
AN1372
The ballast in this reference design consists of four
sections, as shown in Figure 4:
•
•
•
•
High frequency DC/DC converter
Low frequency DC/AC inverter
Ignition circuit
Digital Signal Controller
FIGURE 4:
The DC/DC converter boosts the battery voltage (9V16V) to a high level for the ignition circuit first, and then
drops to ~85V for steady state operation. The DC/AC
inverter converts the DC current to a square wave
current to energize the two lamp electrodes equally.
The high voltage igniter generates high voltage pulses
to strike the lamp. Both The DC/DC converter and the
DC/AC inverter are controlled by a single digital signal
controller.
BLOCK DIAGRAM OF THE DIGITAL REFERENCE DESIGN AUTOMOTIVE HID
BALLAST
Igniter
Battery
Lamp
DC/DC
Converter
DC/AC
Inverter
Vlamp
Ilamp
PWM signal
© 2011-2012 Microchip Technology Inc.
Inverter signal
Digital Signal Controller
DS01372B-page 3
AN1372
AUTOMOTIVE HID BALLAST DIGITAL
DESIGN
System Design Specifications
Table 1 lists the system specifications used for the
automotive HID ballast digital design.
TABLE 1:
SYSTEM DESIGN SPECIFICATIONS
Characteristic
Input Voltage
Specification
Nominal
13.5V
Operation
9V-16V
Temperature Range
Operation
-40ºC to 105ºC
Transient
Maximum input current
Cold lamp: 12A
Hot lamp: 4A
Maximum output current
Maximum input power
Maximum output power
Steady
Conditions
—
2.5A
13.5V, 25ºC
115W
9V-16V, -40ºC to 105ºC
13.5V, 25ºC
75W
9V-16V, -40ºC to 105ºC
Light output
Meet ECE R99
13.5V, 25ºC
Input current
3.5A maximum
13.5V, -40ºC to 105ºC
Output power
35W ±1W
9V-16V, -40ºC to 105ºC
Time of steady light output
≤ 150s
13.5V, 25ºC
Efficiency
> 85%
13.5V
Acoustic Resonance
—
No acoustic resonance
Flicker
—
No flicker
Reliability
Restrike
100%
Successive operation
Input Protection
Output Protection
100 times turn-on/off
3000 hours
Undervoltage protection
9V
Overvoltage protection
16V
Short-circuit protection
Yes
Open circuit protection
Yes
—
Dimension
—
≤10 mm * 60 mm * 80 mm
EMI
—
Meet ECE R10
(error < 20%)
DS01372B-page 4
—
© 2011-2012 Microchip Technology Inc.
AN1372
DC/AC CIRCUIT
Hardware Topology Selection
DC/DC CIRCUIT
The DC/DC converter is the key stage to implement the
control of the lamp voltage, lamp current, and lamp
power. The performance and efficiency of the ballast
are dependent on this stage. As introduced previously,
this stage must have a boost function and large voltage
output capability for open load. The flyback topology
shown in Figure 5 is selected for the minimum number
of components. In addition, voltage and current stress
on the switch is decreased due to the boost function of
the flyback transformer. However, the leakage
inductance of the transformer will generate a highvoltage pulse on the switch, which affects system
power efficiency.
A full-bridge inverter is selected for this stage. Figure 6
shows the full-bridge inverter topology. The operation
frequency of the inverter is dependent on the lamp state.
Before ignition, the inverter runs at a frequency of 1 kHz
for the turn-on and ignition stages. After ignition, the
operation frequency is only 20 Hz for the warm-up stage.
When the warm-up stage is over, the inverter operates
at 200 Hz.
FIGURE 6:
FULL-BRIDGE INVERTER
Vdc
Load
FIGURE 5:
FLYBACK DC/DC
CONVERTER
Vout
IGNITION CIRCUIT
Vin
The automotive HID ballast adopts an ignition circuit,
which is driven by a dual-frequency inverter, as shown
in Figure 7(B). Compared to a conventional ignition
circuit with a voltage doubler, which is shown in
Figure 7(A), it has two main advantages: the first is that
the large ignition capacitor, C1, can be replaced by a
much smaller one (C3 ≤ C1/10), and the second is it
can generate a higher power pulse. This improves the
ignition success rate especially for a hot lamp strike.
FIGURE 7:
IGNITION CIRCUITS
C1
C2
C3
C4
Voltage Doubler
Dual-frequency Inverter
(A)
(B)
© 2011-2012 Microchip Technology Inc.
DS01372B-page 5
AN1372
DIGITAL SIGNAL CONTROLLER
Table 2 shows the dsPIC usage and Table 8 shows the
block diagram of the digital signal controller.
The dsPIC DSC detects the lamp voltage and lamp
current through the Analog-to-Digital Converter
(ADC) pair 0 (AN0 and AN1). Then, the current
reference of the DC/DC converter is calculated
according to the lamp voltage. The controller adjusts
the PWM duty cycle of the DC/DC converter to
control the lamp current. Meanwhile, several fault
signals are monitored by the digital signal controller.
Open circuit protection and short circuit protection
need rapid response, so the internal comparators
(CMP1D and CMP2D) are selected to implement
these two protections. At the same time, the digital
signal controller measures the battery voltage
through the ADC pair 1 (AN2). If the battery voltage
is outside the normal operation range, the ballast will
stop working. In addition, Timer2 of the DSC is used
to control the operation frequency of the full-bridge
inverter, and the inverter drive signal is produced
through the I/O port, RB14.
FIGURE 8:
TABLE 2:
dsPIC® USAGE
Feature
Description
System clock
Internal FRC Oscillator
Input voltage protection
ADC pair 1; Timer2 for
trigger
DC/DC Converter control PWM1
Open and short circuit
protection
CMP1D; CMP2D
Lamp current and voltage ADC pair 0; PWM1 for
sample
trigger
Full-bridge inverter drive
signal
Timer2; RB14
Fail ignition protection
Timer2
Delay function
Timer1
Indication LED
RB4
BLOCK DIAGRAM OF THE DIGITAL SIGNAL CONTROLLER
Ballast Circuitry
Vin
Indication
LED
RB4
PWM1H
AN2
Full-Bridge
PWM
Signal
AN1
AN0
Vlamp
Ilamp
PWM
Ierr
Iref
PI
CMP1D CMP2D
Vmin < Vin < Vmax
Fault
RB14
DS01372B-page 6
DAC Output
Timer2
DAC Output
© 2011-2012 Microchip Technology Inc.
AN1372
(lamp gas switches from isolation to current conductive
state), the ballast should respond quickly and provide
sufficient current to maintain the arc. Constant voltage
control is replaced by constant current control at the
warm-up stage, as shown in Figure 10(B). Finally, at
the run-up stage and steady state, the ballast works in
power control mode. When the lamp voltage exceeds
30V, it enters into the run-up stage. The ballast should
control the lamp power from a high level (~75W,
depending on the lamp status) to a low level (35W) until
steady state. During this stage the decreasing power
control mode is selected. When the lamp voltage
exceeds 65V, the lamp enters into a steady state. The
ballast operates at constant power control to maintain
the lamp power at 35W, ±1W. The steady state
schematic is illustrated in Figure 10(C).
Control Strategy and Control Loop Design
CONTROL STRATEGY DESIGN
As introduced in the section “Technical Background
of Automotive HID Ballast”, the start-up process of
the automotive HID lamps consists of six stages. It
needs different control strategies in every stage and
the timing control is very strict. Figure 9 shows the
timing flowchart of the control strategies.
At the turn-on stage, the ballast should boost the
battery voltage to a proper level. This voltage is
maintained for a period of time to fully charge the igniter
capacitor, until the lamp gas switches from isolation to
current conductive state. The DC/DC stage works in
constant voltage control in this mode, as shown in
Figure 10(A). Immediately after successful ignition
St
at
e
R
St
ea
dy
un
-u
p
W
ar
m
-u
p
Ta
ke
ov
er
Ig
ni
tio
n
TIMING FLOWCHART OF THE CONTROL STRATEGIES
Tu
rn
-o
n
FIGURE 9:
r
C
on
s
C tan
on t P
tro o
l we
er
ec
re
C asin
on g
tro P
l ow
t
D
C N
on o
tro
l
C
C on
C urr sta
on en n
tro t t
l
C N
on o
tro
l
C
o
Vo ns
C lta tan
on g t
tro e
l
Vlamp
Note:
FIGURE 10:
This figure shows the “as is” magnitude profile of the lamp. Its direction is not illustrated here.
VOLTAGE, CURRENT AND POWER CONTROL DIAGRAMS (A, B, AND C)
Co
Co
K1
Verr
ko
(B)
K2
Ierr
Vlamp
Gi
Constant Voltage
Control Mode
(A)
ko
Vref
Ilamp
Gi
Constant Current
Control Mode
Iref
Co
K1
(C)
K2
ko
Perr
Gi
Power Control Mode
© 2011-2012 Microchip Technology Inc.
MULT
Plamp
Pref
DS01372B-page 7
AN1372
Three different control modes (voltage, current, and
power) are needed during the start-up process, which
makes the software quite complex. However, the
features of the dsPIC DSC minimize the complexity of
the software design. For example:
• Interrupt driven control with multiple priorities
• Intelligent peripherals to minimize software
overhead
• High performance math and DSP engine to
efficiently perform complex calculations
• Built-in comparators to provide high-speed,
reliable protection
• Simultaneous sampling ADC for accurate power
measurements
In addition, there are two transitions between two
control mode changes in the process. The first
transition is between the voltage control mode and
current control mode. This may delay the current
response of the DC/DC converter after ignition, which
may lead to the lamp arc becoming extinguished. The
second transition is between the current control mode
and power control mode, which will lead to instability of
the lamp current. Considering this, the control mode is
optimized in this reference design. Only current control
mode is employed for the entire start-up process. An
advanced scheme is implemented using the dsPIC
DSC, which achieves the various control modes
without the drawbacks of unstable lamp current or
extinguishing of the ignition arc.
First, the constant voltage control mode in the turn-on
stage is replaced by the constant current control mode.
The maximum output voltage of the DC/DC converter
is limited by the cycle-by-cycle Current-Limit function of
the digital signal controller’s PWM module. The limited
voltage value should be set for the ignition circuit
(somewhere between 360V to 400V for igniter circuitry
components tolerance). This accelerates the current
response of the DC/DC converter, and contributes to a
high ignition success rate. Also, the takeover current
supplied by the auxiliary current circuit is reduced;
therefore, the auxiliary current capacitor can be a
smaller one.
EQUATION 3:
CURRENT REFERENCE
FORMULA
P ref
I ref = -------------V lamp
Where:
Iref is the lamp current reference
Pref is the lamp power reference
Vlamp is the lamp voltage
During these two stages (Run-up and Steady), the
power reference is determined by lamp voltage
sampled by the digital signal controller’s ADC module.
The relationship between the power reference and
lamp voltage is shown in Figure 11.
FIGURE 11:
POWER REFERENCE AND
LAMP VOLTAGE
Pref
58W
35W
30V
Where:
65V
Vlamp
Pref is the lamp power reference
Vlamp is the lamp voltage
As discussed previously, the current reference of the
regulator during the entire start-up process is shown in
Figure 12.
Next, the power control mode is replaced by the current
control mode in the run-up stage and steady state.
When the start-up process enters into the run-up stage
from the warm-up stage, there is no control mode
transition, which may lead to instability of the lamp
current. In this way, we can control the lamp current to
achieve lamp power control. The current reference in
these two stages is calculated, as shown in Equation 3.
DS01372B-page 8
© 2011-2012 Microchip Technology Inc.
AN1372
St
at
e
R
St
ea
dy
un
-u
p
W
ar
m
-u
p
Ta
ke
ov
er
Ig
ni
Iref
tio
n
CURRENT REFERENCE
Tu
rn
-o
n
FIGURE 12:
1.8A
0.8A
0.41A
t
CURRENT CONTROL LOOP DESIGN
EQUATION 4:
The full-bridge inverter converts the DC voltage into
low-frequency square wave AC in a fully symmetrical
pattern. Therefore, the small signal modeling of the
ballast will only be conducted on the flyback converter.
As introduced in the section “Control Strategy and
Control Loop Design”, there is only a current loop in
this reference design. Figure 13 shows the block
diagram of the current loop.
G ( s ) = Gm ( s ) ⋅ Gp ( s ) ⋅ H ( s )
Where:
Gm(s) is PWM generator function
Gp(s) is the power stage function
H(s) is the feedback function
Table 3 lists the design parameters of the current loop
at steady state.
TABLE 3:
Value
Output Power
Po = 35W
Output Current
Io = 0.41A
Input Voltage
Vi = 13.5V
fs = 180 kHz
Operation Frequency
Current Loop Sampling Frequency
f = 180 kHz
Primary Inductance
Lp = 3.47 µH
Duty Cycle
D = 0.51
Turn Ratio
n=6
fsw = 200 Hz
Current Loop Bandwidth
FIGURE 13:
Iref
The PWM generator function Gm(s) = 1/8. The
feedback function consists of two parts, one is the
sample resistance (0.68Ω) and the other is the
proportional amplifier (gain is 2). Therefore, the value
of H(s) is 1.36. The power stage function, Gp(s), is
calculated by the flyback small signal module as shown
in Figure 14.
CURRENT LOOP DESIGN
PARAMETERS
Design Parameter
ORIGINAL TRANSFER
FUNCTION
CURRENT LOOP BLOCK DIAGRAM
+
Ierr
Compensator
(GI)
Vc
PWM
Gm(s)
d
Power Stage
Gp(s)
Lamp
I
H(s)
© 2011-2012 Microchip Technology Inc.
DS01372B-page 9
AN1372
FIGURE 14:
SMALL SIGNAL MODEL OF THE FLYBACK CONVERTER
L
Ig(t)
(Vg+V/n) * d(t)
+
I(t)
1:D
1-D:n
V(t)
R
C
Vg(t)
I * d(t)/n
Ig d(t)
–
Based on Figure 14, the power stage function, Gp(s), is
calculated in Equation 5. As a result, the entire original
transfer function is calculated, as shown in Equation 6.
EQUATION 5:
POWER STAGE TRANSFER FUNCTION
Lp
D′----– -------------- s
V
D
D′
⋅R
o
v ( t )G p ( s ) = -----------= ------ ⋅ -------------------------------------------------------2
R ⋅ dt Vg (t)= 0 R
2
2 n Lp
2
n L p Cs + ----------- s + D′
R
EQUATION 6:
Where:
Vo = the input voltage
D = the duty cycle
D' = (1-D)
R = the lamp equivalent resistance
Lp = the primary inductance
ENTIRE ORIGINAL TRANSFER FUNCTION
Lp
D′
------ – -------------s
Vo
1.36
D D′ ⋅ R
- ⋅ ---------G ( s ) = G m ( s ) ⋅ G p ( s ) ⋅ H ( s ) = ------ ⋅ -------------------------------------------------------2
8
R
n
L
2
2
2
p
n L p Cs + ----------- s + D′
R
EQUATION 7:
Where:
Gm(s) = PWM module transfer function
H(s) = Feedback circuitry transfer function
CURRENT ERROR COMPENSATOR
The transfer function for the current error compensator is given by:
k Ii
1 + T co ⋅ s
G I ( s ) = k pi + ------ = k pi ⎛------------------------ ⎞
⎝ T co ⋅ s ⎠
s
Where fz = 20 Hz, which is the location of zero for the current PI controller and,
1
T co = ---------- = 0.00796
2πf z
′2 2
1 + T co ⋅ s
nL p CD R f sw 8
G I ( s ) = ------------------------------------ ⋅ ---------- ⋅ ⎛⎝------------------------ ⎞⎠
T co ⋅ s
Vo Lp
1.36
1 + 0.00796 ⋅ s
⇒ G I ( s ) = 0.1162 ⋅ ⎛----------------------------------- ⎞
⎝ 0.00796 ⋅ s ⎠
14.59
⇒ G I ( s ) = 0.1162 + ------------s
Based on Equation 7,
kpi = 0.1162 and kIi = 14.59/Sampling Frequency = 0.00008.
DS01372B-page 10
© 2011-2012 Microchip Technology Inc.
AN1372
Figure 15 shows bode plots of the original transfer
function and compensated transfer function.
FIGURE 15:
ORIGINAL AND COMPENSATED BODE PLOTS
Original Functions (Gain Margin 33.83 dB, Phase Margin 15.2º)
Compensated Functions (Gain Margin 48.43dB, Phase Margin 101.7°)
© 2011-2012 Microchip Technology Inc.
DS01372B-page 11
AN1372
SOFTWARE DESIGN
Figure 16 shows the control flowchart of the system.
FIGURE 16:
CONTROL FLOWCHART
Initialization
Yes
Vin < 9V
or Vin > 16V?
Turn OFF
Converter
No
Turn ON Converter
and Control the
Output Voltage
at 360V
Timer1 Start to Count
No
Ignition
successful?
No
Yes
Exceed
10 seconds?
Yes
DC
Operation
Yes
Constant
Power
Control
Vlamp > 65V?
No
Decreased
Power Control
DS01372B-page 12
No
Open or Short
Circuit?
Yes
© 2011-2012 Microchip Technology Inc.
AN1372
Timing Logic for Software
Implementation
Timer1 runs at a frequency of 1 kHz. It is the time base
for the delay subroutine function, which is used in the
ignition failure detection. Timer2 is used for the fullbridge inverter drive signal and runs at a different
frequency.
PWM1 runs at 180 kHz. It also triggers ADC pair 0
every eight cycles. Lamp voltage and lamp current are
sampled by ADC pair 0. An ADC interrupt is served on
every trigger. In the Interrupt Service Routine (ISR), the
digital signal controller reads the ADC result, checks
the lamp status, executes the compensator, and then
updates the PWM duty cycle to deliver proper power to
the lamp. The timing diagram is illustrated in Figure 17.
Before ignition, Timer2 runs at a frequency of 2 kHz to
charge the igniter capacitor. After ignition, Timer2 runs
at 40 Hz to warm-up the lamp electrode. After the
warm-up stage, Timer2 runs at 400 Hz and remains at
this frequency. In addition, Timer2 triggers ADC pair 1
every period to sample the battery voltage.
FIGURE 17:
TIMING LOGIC
Timer1
Counter
1 kHz
Timer2
Counter
2 kHz
40 Hz
400 Hz
Trigger
ADC Pair 1
PWM1
© 2011-2012 Microchip Technology Inc.
180 kHz
DS01372B-page 13
AN1372
If the ignition flag = 0, the program flows into the ignition
check function. If the ignition is detected, the ignition
flag is set. The Timer2 period is reconfigured to 40 Hz
for warm-up operation. Then, the program flows into
the warm-up function. If the ignition is not detected, the
program jumps to the open loop control flow.
Software Flow
The software flow is shown in Figure 18.
At power-up, all of the variables and peripherals are
initialized. PWM1 is configured to run at 180 kHz.
Timer1 and Timer2 are configured to 1 kHz and 2 kHz
separately. On every period, Timer2 generates an
interrupt. Output pin RB14 is toggled in the interrupt
service routine to provide the PWM for the Full-Bridge
MOSFETs. Ignition time-out and warm-up completion
detection is also implemented in this interrupt service
routine. ADC pair 1 is also triggered by Timer2.
However, its result is read and checked in background
to detect whether the battery voltage is in the expected
range.
If the ignition flag = 1, warm-up code is executed. After
the warm-up stage the lamp voltage is checked. If the
lamp voltage is larger than 65V, the program jumps to
the constant power control flow. A fixed power
reference (35W) is divided by lamp voltage. The result
is fed to the current compensator as the current
reference. If the lamp voltage is smaller than 65V, the
program flows to decreased power control flow. A
variable power reference, as illustrated in Figure 11, is
divided by the lamp voltage. The result is feed to the
current compensator as the current reference. The
compensator is then executed, and feeds its result to
the PWM module.
On every PWM cycle, PWM1 triggers ADC pair 0 to
sample the lamp current and voltage, and most of the
control algorithm is implemented in the ADC pair 0
interrupt service routine. An ignition success flag is
checked at the entrance of the interrupt service routine.
FIGURE 18:
SOFTWARE FLOW
Initialize
Compensators
Initialize
Peripherals
Reset
e
gg
Tri
D
rA
air
Cp
0
Turn ON
PWM1 Module
Wait for
ADC0
Interrupt
Turn ON
Timer2
Trigger ADC pair 1
VIN
DS01372B-page 14
Wait for
Timer2
Interrupt
Check
Input
Voltage
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE 19:
TIMER2 INTERRUPT SERVICE ROUTINE (ISR) FLOW
Timer2
Interrupt
Toggle
Inverter
Drive
Signal
Check End
of Warm-up
Stage
© 2011-2012 Microchip Technology Inc.
Check
Ignition
Failure
DS01372B-page 15
AN1372
FIGURE 20:
ADC INTERRUPT SERVICE ROUTINE (ISR) FLOW
Ignition Flag = 0
ADC0
Interrupt
Ignition Flag = 1
Startup_Phase_Operation:
Open_Loop:
g!
=2
Decreased_power_control:
Warm-up
Stage
Current
Compensator
Calculate
Iref
PWM
Current
Loop
Compensator
Filter Lamp
Voltage
Feedback
Signal
Vlamp
Vlamp < 65V
Calculate
Iref
Decreased_Voltage_control:
Bu
s_
Wa
rm
Update
Inverter
Frequency
St
Confirm_Ignition:
Co
V
ns
la
ta
nt mp >
_c
on 65V
tr
ol
_O
pe
ra
ti
on
:
PWM
Bus_Warmup_Success_Flag = 2
up
_S
uc
ce
ep
ss_
_u
F la
p:
Ilamp > 0.3A
Ila
Ope mp < 0
.3
n_C
ont A
rol
:
Ignition
Check
Voltage
Loop
Compensator
Ilamp
Filter Lamp
Current
Feedback
Signal
Ilamp
Current
Loop
Compensator
PWM
Legend: Text in red indicates labels in the Assembly code.
Text in black indicates jump conditions.
DS01372B-page 16
PWM
© 2011-2012 Microchip Technology Inc.
AN1372
Functions Used in Software
The functions listed in Table 4 and Table 5 are used in
software for implementing the various stages of the
automotive HID lamp ballast.
TABLE 4:
SOFTWARE FUNCTION
File Name
main.c
Function Name
Description
Digital signal controller frequency configuration.
main()
Auxiliary clock configuration.
PWM, CMP, and ADC configuration.
Compensator initialization.
Enable the PWM and ADC.
Enable the full-bridge drive.
Check the input voltage fault.
init.c
init_FlybackDrive()
PWM1 module configuration.
init_CMP()
CMP1D and CMP2D configuration.
init_ADC()
ADC pair 0 and ADC pair 1 configuration.
init_FlybackCurrentCtrl()
Initialize flyback compensator.
Delay_ms
Time delay configuration.
init_Timer2_full_bridge_drive() Full-bridge inverter drive signal configuration.
isr.c
Init_Variables()
Reset variables and flags.
Init_IO()
Initialize RB14 as output for full-bridge PWM signal.
T1Interrupt()
Increment interrupt counter.
T2Interrupt()
Toggle I/O.
Ignition time-out check.
End of warm-up check.
FlybackCurrentCntrl()
isr_asm.s
TABLE 5:
Refer to Table 5.
isr_asm.s FUNCTION
File Name
isr_asm.s
Flyback compensator.
Section Label
Description
Startup_Phase_Operation
Filter lamp current.
step_up
Warm-up current control.
Decreased_power_control
Filter lamp voltage.
Provide current reference by lamp voltage condition.
Decreased_current_control
Run-up stage current loop control.
Power_Control_Operation
Current reference calculation.
Power loop control.
Open_Loop
Ignition success check.
Open_control
Open voltage control.
Confirm_ignition
Set ignition success flag.
Configures DC operation frequency.
Filters initialization.
© 2011-2012 Microchip Technology Inc.
DS01372B-page 17
AN1372
HARDWARE DESIGN
Power Stage Parameter Design
System Block Diagram
TABLE 6:
Figure 21 shows the system circuit diagram of the
reference design. As introduced in the section
“Hardware Topology Selection”, the design consists
of four major sections. In addition, the design also
includes several auxiliary circuits.
An EMI filter at the input side attenuates the
Electromagnetic Interference (EMI). At the same time,
a reverse input-voltage protection circuit is also at the
input side. Moreover, an RCD auxiliary current circuit
before the full-bridge inverter provides the major takeover current before the response of the converter. A
signal filter adjusts the lamp voltage and current signals
before the ADC. Finally, the auxiliary power system
supplies the digital and analog ICs on the board.
FLYBACK DESIGN DATA
Design Parameter
Rated input voltage
Vin = 13.5V
Minimum input voltage
Vin_min = 9V
Maximum input voltage
Vin_max = 16V
Rated output voltage
Vo = 85V
Minimum output voltage
Vo_min = 30V
Maximum output voltage
Vo_max = 102V
Rated output current
Maximum output current
Rated output power
Maximum output power
Operation frequency
DS01372B-page 18
Value
Io = 0.41A
Io_max = 1.8A
Po = 35W
Po_max = 75W
fs = 180 kHz
System efficiency
η = 85%
Diode forward voltage
Vf = 1V
© 2011-2012 Microchip Technology Inc.
SYSTEM CIRCUIT DIAGRAM
T1
EMI
Filter
Aux. Power
R4
R1
D1 V
in
Auxiliary
Current Circuit
D3
C3
12V
R4
D2
Q5
D6
C4
Q4
Q6
D5
R6
Q2
Reverse
Protection
Vlamp
Ilamp
PWM
Signal
dsPIC®
PWM
Driver
DSC
Lamp
Arc gap
T2
C5
D4
R5
R3
R5
Vin
Inverter
Driver
Signal
Ignition
Circuit
Q3
Q4
Q5
Q6
In this design, the input inrush current at the start of ignition is not controlled. To reduce this inrush current, it is recommended to use the internal
comparator of the dsPIC device. The comparator should be set as the trigger source of the PWM Current-Limit mode.
AN1372
DS01372B-page 19
Note:
Q3
D7
C2
R2
Q1
Vdc
Driver
© 2011-2012 Microchip Technology Inc.
FIGURE 21:
AN1372
CALCULATION OF THE TRANSFORMER
TURNS RATIO n
EQUATION 8:
MAXIMUM DRAIN-TOSOURCE VOLTAGE Vds_max
OF MOSFET
V ig
V ds_max = V in_max + ------- + V′
n
Where:
EQUATION 10:
CURRENT PARAMETERS
OF THE PRIMARY
INDUCTOR
According to the power conservation, the average
input current is:
Po
I in_ave = ---------------V in ⋅ η
Where:
Rated output power: Po = 35W
Rated input voltage: Vin =13.5V
Output voltage for ignition circuit: Vig = 360V
System efficiency: η = 85%
Max input voltage: Vin_max = 16V
The average current during the on period is:
Overshoot voltage: V’ ≈ 15V
I in_ave
I ave_on = --------------D
Max drain-to-source voltage of MOSFET: VDSS = 100V
Max drain-to-source voltage: Vds_max = 90% * VDSS = 90V
Based on Equation 8, the transformer turns ratio is
n = 6.
Where:
Duty cycle: D = 0.51
The peak current of the primary inductor is:
ΔI
I L_pk = I ave_on + -----2
CALCULATION OF THE PRIMARY INDUCTOR Lp
EQUATION 9:
VOLTAGE RATIO Vin/Vo OF
THE CONVERTER AT
RATED OPERATION
Where:
Assumed inductor ripple current: ΔI = 11A
The RMS current of the primary inductor is:
n ⋅ V in ⋅ D
V o = -----------------------1–D
Where:
Rated input voltage: Vin = 13.5V
Rated output voltage: Vo = 85V
Duty cycle: D
Calculated turns ratio: n = 6
Based on Equation 9, the duty cycle at rated operation
D = 0.51.
D
I L_rms = I L_pk ⋅ ---3
Based on Equation 10, the average input current
Iin_ave = 3.05A, the peak current of the primary inductor
IL_pk = 11.48A, and the RMS current of the primary
inductor IL_rms = 4.73A.
EQUATION 11:
VALUE OF THE PRIMARY
INDUCTOR
V in ⋅ t on
L p = ------------------ΔI
The flyback converter works at CCM mode at rated
operation.
Where:
Rated input voltage: Vin = 13.5V
Turn on time: ton = D * (1/fs) = 2.83 µs
Inductor ripple current: ΔI = 11A
Based on Equation 11, the primary inductor Lp = 3.47
µH.
DS01372B-page 20
© 2011-2012 Microchip Technology Inc.
AN1372
SELECTION OF THE PLANAR CORE
The magnetic core cannot be saturated; therefore, the
worst conditions (i.e., Vin = 9V; Po = 75W; Vo = 30V)
should be considered.
Based on Equation 9, the duty cycle at the worst
condition Dw = 0.357.
Based on Equation 10, the average input current
Iin_ave_w = 9.8A, and the average on current Iave_on_w =
27.46A.
EQUATION 12:
THE INDUCTOR RIPPLE
CURRENT AT WORST
CONDITION
ΔI w
V in_min ⋅ D w
= -----------------------------fs ⋅ Lp
Comparing the Magnetics planar cores, FR43208EC
and FR43208IC are selected for the flyback
transformer, as shown in Equation 14.
EQUATION 14:
4
AP = A w ⋅ A e = 0.767cm > 0.72cm
4
Where:
Aw = 58.99 mm2
Ae = 130 mm2
CALCULATION OF THE PRIMARY AND
SECONDARY TURNS
EQUATION 15:
Where:
Minimum input voltage: Vin_min = 9V
PARAMETERS OF THE
SELECTED PLANAR CORES
THE PRIMARY AND
SECONDARY TURNS
The primary turns is:
Duty cycle at worst condition: Dw = 0.357
L p ⋅ I L_pk_w
N p = --------------------------ΔB ⋅ A e
Operation frequency: fs = 180 kHz
Primary inductor: Lp = 3.47 µH
Where:
Based on Equation 12, the inductor ripple current at the
worst condition ΔIw = 5.14A.
Based on Equation 10, the peak current of the primary
inductor at the worst condition IL_pk_w = 30.03, and the
RMS current of the primary inductor at the worst
condition IL_rms_w = 10.36A.
The primary inductor: Lp = 3.47 µH
The peak current of the primary inductor at worst
condition: IL_pk_w = 30.03A
Saturation magnetic induction: ΔB = 0.3T
Ae = 130 mm2
The planar core is selected using the AP calculation
method, as shown in Equation 13.
The secondary turns is:
EQUATION 13:
Where:
THE VALUE OF AP
The primary side AP is:
Ns = n ⋅ Np
Turns ratio: n = 6
2
8
6.33 ⋅ L p ⋅ d p ⋅ 10
4
AP p = ---------------------------------------------- ( cm )
ΔB
Where:
The primary inductor: Lp = 3.47 µH
The primary wire diameter: d2p = 1.816 mm
Based on Equation 15, the primary turns Np = 2.65, the
selected Np = 2, and the selected second turns Ns = 12.
CALCULATION OF THE TRANSFORMER GAP
EQUATION 16:
TRANSFORMER GAP
Saturation magnetic induction: ΔB = 0.3T
2
The second side AP is:
L gap
APs ≈ ( 2 ∼ 3 ) ⋅ AP p
μ0 ⋅ Np ⋅ Ae
= --------------------------Lp
Where:
The entire AP is:
AP = AP p + AP s
Based on Equation 13, the entire AP = 0.72 cm4.
The primary turns: Np = 2
Ae = 130 mm2
The primary inductor: Lp = 3.47 µH
Based on Equation 16, the transformer gap Lgap = 0.19
mm.
© 2011-2012 Microchip Technology Inc.
DS01372B-page 21
AN1372
POWER COMPONENTS SELECTION
Ignition Circuit Parameter Design
• MOSFET Q1 for input voltage reverse protection
The selected ignition circuit is driven by a dualfrequency inverter, the design parameters are shown in
Table 7.
EQUATION 17:
CALCULATION OF THE
MAJOR MAXIMUM
PARAMETERS
The maximum RMS drain current is:
I D_rms_max = I L_rms_w = 10.36A
TABLE 7:
IGNITION CIRCUIT DESIGN
PARAMETERS
Design Parameter
Value
Rated input voltage
Vig = 360V
Based on Equation 17, FDD8896 is selected for Q1,
VDSS = 30V, Rds_on = 5.7 mΩ.
Breakover voltage of the gas
discharge tube
• MOSFET Q2 for flyback converter
Ignition pulse voltage value
EQUATION 18:
CALCULATION OF THE
FLYBACK MOSFET
MAXIMUM PARAMETERS
The maximum drain current is:
I D_max = I L_rms_w = 10.36A
The maximum drain to source voltage is:
V ig
V ds_max = V in_max + ------- = V′ = 90V
n
Based on Equation 18, FDB3652 is selected for Q2,
VDSS = 100V, Rds_on = 16 mΩ.
CALCULATION OF THE
FLYBACK DIODE MAXIMUM
PARAMETERS
The maximum forward current is:
I L_pk_w
I F_max = ----------------- = 5A
n
Tw > 0.5 µs
Inverter frequency for ignition
fig = 1 kHz
IGNITER CAPACITOR AND RESISTOR
Considering the ignition energy, the resonance
capacitance C4 = 33nF/630V.
EQUATION 21:
T discharge ≈ T charge = 5 ⋅ C5 ⋅ R5
The charge and discharge period is:
1
T ig = ----f ig
Where:
Inverter frequency for ignition: fig = 1 kHz
In addition, the charge time and C5 should meet:
T ig
T charge < ------2
V R_max = V ig + V in_max ⋅ n = 504V
• MOSFET Q3-Q6 for full-bridge inverter
EQUATION 20:
CALCULATION OF THE
FULL-BRIDGE MOSFET
MAXIMUM PARAMETERS
V ds_max
C4
C 5 ≤ -----10
CALCULATION OF TRANSFORMER
EQUATION 22:
CALCULATION OF TURN
RATIO N
V ig_pulse
n > -------------------V break
I D_max = I o_max = 1.8A
V ig
= ------- = 180V
2
and
Based on Equation 21, the selected pump capacitance
C5 = 33nF/630V and the selected charge resistance
R5 = 1k/3W.
The maximum drain current is:
The maximum drain to source voltage is:
CALCULATION OF PUMP
CAPACITANCE C5 AND
CHARGE RESISTANCE R5
The charge and discharge time are almost the same:
The maximum reverse voltage is:
Based on Equation 19, RHR660 is selected for D3,
VR_max = 600V, IF(AV)_max =6 A, Qrr = 45 nC.
Vig_pulse > 25 kV
Ignition pulse width
• Diode D3 for flyback converter
EQUATION 19:
Vbreak = 600V
Where:
Ignition pulse voltage value: Vig_pulse > 25 kV
Breakover voltage of the gas discharge tube: Vbreak = 600
Based on Equation 19, FCD7N60 is selected for Q3Q6, VDSS = 650V, ID_rms_max = 7A, Rds_on = 0.53Ω.
DS01372B-page 22
© 2011-2012 Microchip Technology Inc.
AN1372
Based on Equation 22, the turns ratio n > 41.7.
Considering the parasitic parameters, the selected
turns ratio n = 80.
FIGURE 22:
EQUATION 24:
RMS IGNITION PULSE
WIDTH
THE POWER OF THE 15V
AUXILIARY POWER
CIRCUIT
2
1
P = --- L p_leak ⋅ I L_pk ⋅ f s
2
Where:
sin ( Wd ⋅ t ) = 0.707
The leak inductor of the primary inductor: Lp_leak = 0.1 µH
The peak current of the primary inductor: IL_pk = 11.48A
Operation frequency: fs = 180 kHz
Based on Equation 24, the power of the 15V auxiliary
power, P = 1.18W.
FIGURE 23:
AUXILIARY POWER
SYSTEM CIRCUITS
MCP1703
Vbat
EQUATION 23:
CALCULATION OF THE
PRIMARY INDUCTOR Lp
3.3V
Cin
Cout
The RMS ignition pulse width is shown in Figure 22.
sin ( Wd ⋅ t ) = 0.707
Where:
3.3V Auxiliary Power Circuit
1
Wd = --------------------L p ⋅ C4
T1
the resonance frequency is:
⇒ Wd ⋅ t 1 = 0.24π, Wd ⋅ t 2 = 0.76π
15V
and the ignition pulse width is:
0.76π – 0.24π
T w = t 2 – t 1 = ---------------------------------- > 0.5μs
Wd
Based on Equation 23, the primary inductor Lp > 0.28
µH, the selected Lp = 0.28 µH, and the selected
Ls = 1.78 mH.
15V Auxiliary Power Circuit
System Auxiliary Circuits Design
AUXILIARY POWER SYSTEM DESIGN
There are two auxiliary powers, one is 3.3V which
supplies the digital signal controller and the op amp.
The other is 15V, which supplies the full-bridge
MOSFET driver. Figure 23 shows the circuit of the
auxiliary power system.
The power of the 15V circuit is calculated by
Equation 24.
© 2011-2012 Microchip Technology Inc.
DS01372B-page 23
AN1372
MOSFET DRIVER DESIGN
SIGNAL FILTER DESIGN
There are five drive signals in the design, one is the
flyback MOSFET drive signal and the other four are the
full-bridge inverter MOSFETs. A MCP1407 IC is used
to drive the flyback MOSFET. A IR2453 IC is used to
drive the four full-bridge MOSFETs. The dead time is
fixed at 1 µs. Figure 24 shows the two drive circuits.
An op amp is used the amplify and filter the lamp
voltage and current feedback signals. Figure 25 shows
the two signal filters. Equation 25 calculates the
transfer function of the two filters.
FIGURE 24:
MOSFET DRIVER CIRCUITS
VCC
VCC
Rt
Vbat
1
Digital
Controller
Signal
Digital
Controller
Signal
VDD
VDD
Input
OUT
OUT
NC
GND
GND
MCP1407
Drive Signal
HO1
HO1
VB1
VS1
VS1
LO1
Ct
LO1
HO2
HO2
VB2
SD
Flyback MOSFET Driver Circuitry
GND
VS2
VS2
LO2
LO2
IR2453
Full-bridge MOSFETs Driver Circuitry
FIGURE 25:
SIGNAL FILTER CIRCUITS
Lamp Voltage
Sample Signal
Vi
R1
C1
+
R2
R6
Vo
Lamp Current
Sample Signal
Vo
+
C2
Vi
Lamp Voltage Feedback
EQUATION 25:
R5
-
R3
R4
C3
Lamp Current Feedback
THE TRANSFER FUNCTION OF THE TWO FILTERS
The voltage filter transfer function is:
Vo
1
------ = -----------------------------------------------------------------------------------------------2
Vi
C1 C2 R1 R2 ⋅ s + ( C2 R1 + C2 R2 ) ⋅ s + 1
The current filter transfer function is:
R5 + R6
Vo
1
------ = -----------------⋅ ----------------------------R5
Vi
C3 R3 ⋅ s + 1
DS01372B-page 24
© 2011-2012 Microchip Technology Inc.
AN1372
GETTING STARTED
Application Code Programming
Figure 26 shows an overhead view of the
demonstration panel. Inside the demonstration case,
there is a 12 VDC/6.5 AH gel cell battery as well as a
battery charger, which enables stand-alone operation.
The MPLAB® ICD 2, MPLAB ICD 3, PICkit™ 3, and
MPLAB REAL ICE™ in-circuit emulators may be used
along with MPLAB IDE to debug and program your
software. MPLAB IDE is available for download from
the Microchip web site.
1.
2.
3.
Xenon HID lamp.
Igniter.
dsPIC33FJ06GS202 Digital Ballast Board:
Special software interacts with the MPLAB IDE
application to run, stop, and single-step through programs. Breakpoints can be set and the processor can
be reset. Once the processor is stopped, the register’s
contents can be examined and modified. For more
information on how to use MPLAB IDE, refer to the
following documentation:
A green LED on the Ballast Board, when lit,
indicates that the 3.3V control circuitry power is
available.
A red LED on the Ballast Board, when lit, indicates
that the battery voltage is too low to support board
operation. When this occurs, set the power ON/
OFF switches to the OFF position and connect a
power cord to the battery charger socket.
Note:
4.
5.
6.
• “MPLAB® IDE User’s Guide” (DS51519)
• “MPLAB® IDE Quick Start Guide” (DS51281)
• MPLAB® IDE Help
The dsPIC33FJ06GS202 Digital Ballast
Board does not control the Hi/Lo beam
function.
AC power input socket.
Power ON/OFF switch.
Beam HI/LO switch.
FIGURE 26:
DEMONSTRATION PANEL AND COMPONENTS
2
4
3
1
5
© 2011-2012 Microchip Technology Inc.
6
DS01372B-page 25
AN1372
Programming the Application
Complete the following
demonstration board:
1.
2.
steps
to
Running the Application Demonstrations
program
the
Make sure that the Power ON/OFF switch is in
the OFF position.
Connect the emulator header to the 6-pin
connector labeled ICD_1.
FIGURE 27:
EMULATOR CONNECTOR
POSITION
This section describes two different automotive
headlight demonstrations:
• HID lamp operation with full digital control
• Hi/Lo-beam operation
Both of these demonstrations can be run either
simultaneously or separately using the following steps
(refer to Figure 26 for switch locations):
1.
To operate the HID lamp, use the Power ON/
OFF switch.
When the lamp is switched on, a high-pitched
buzzing noise may be present at the start of
ballast operation. This is normal and is not a
cause for concern.
2.
3.
4.
5.
6.
7.
8.
9.
Set the Power ON/OFF switch to the ON
position.
Start MPLAB IDE and open the HID Ballast
demonstration project by double-clicking
the .mcw file. The remaining steps take place
within MPLAB IDE.
Build the project by selecting Project > Build All.
Choose the desired programmer, such as
MPLAB ICD 3, by selecting Programmer >
Select Programmer.
Program the device by selecting Programmer >
Program.
After the device has been programmed, set the
Power ON/OFF switch to the OFF position.
Disconnect the emulator header from the 6-pin
connector labeled ICD1_1.
The HID Ballast board is now programmed and ready
to run the demonstration.
Note:
When debugging the HID Ballast with the
emulator, the connection between the PC
and the board can be lost due to noise
interference from lamp ignition. Therefore,
it is recommended to use Programming
mode.
DS01372B-page 26
3.
4.
To check hot lamp operation, do the following:
a) Run the lamp for at least one minute to
bring the lamp to a high temperature.
b) After one minute, turn the HID lamp off by
setting the Power ON/OFF switch to the
OFF position.
c) Wait for a few seconds and then set the
Power ON/OFF switch to the ON position.
The lamp should light immediately.
To check cool lamp operation, do the following:
a) Make sure the HID lamp is cold. The lamp
should be switched to the OFF position for
at least 10 minutes.
b) Set the Power ON/OFF switch to the ON
position. The lamp should light immediately.
To run the Hi/Lo-beam demonstration, simply
toggle the Hi/Lo-beam ON/OFF switch.
Warning: When the lamp is lit, the light emitted is
very strong, which may cause physical
harm to your eyes.
In addition, the lamp tube may rise to a
very high temperature in just a few seconds. Do not touch the lamp or allow
any flammable objects to come in
contact with the lamp tube.
FAILURE
TO
HEED
THESE
WARNINGS COULD RESULT IN
PROPERTY DAMAGE OR BODILY
HARM.
© 2011-2012 Microchip Technology Inc.
AN1372
LABORATORY TEST RESULTS AND
WAVEFORMS
Table 8 summarizes the resources required by the HID
Ballast design in terms of memory size, peripherals,
MIPS, etc.
TABLE 8:
dsPIC RESOURCE USAGE
Resource
Value
Program Memory
2409 bytes
Data Memory
48 bytes
PWM
1 channel
ADC
3 channels
Comparator
2 channels
MIPS
33.6
I/O
TABLE 9:
2 channels
The final prototype of the automotive HID ballast was
tested according to the technical requirements. The
test results are shown in Table 9. The testing conditions
are as follows:
• Test lamp: Xenon HID lamp, 35W, color
temperature 6000K.
• Ambient temperature: 25ºC, ±5ºC
• Test input voltage: 9V-16V
• Rated voltage: 13.5V
• Oscilloscopes: YOKOGAWA DLM2024
• Voltage source: Chroma 62024P-80-60
Figure 28 through Figure 37 show the various
waveforms including lamp current, voltage and power
from the turn-on stage to the steady state, and provides
a magnified view in every stage. In addition, the ignition
curve and the input current curve are shown to verify
the reference design.
TEST RESULTS
Characteristic
Input Voltage
Temperature
Transient
Test Result
Comments
Nominal (13.5V)
Operation (9V-16V)
Passed
Passed
—
Operation (-40ºC to 105ºC)
Passed
—
VIN = 9.4V-16V
VIN = 9.4V
Maximum Output Current
1.8A
Maximum Input Power
101W
Maximum Output Power
Light Output
Steady
Input Current
Output Power
Time to reach steady light output
Efficiency
Acoustic Resonance
82.5W
78W
83.5W
70.2W
67.2W
3A
35W
Passed
85.91%
No
Flicker
Restrike
Reliability
Successive Operating
Undervoltage Protection
Overvoltage Protection
Short Circuit Protection
Passed
9.4V
16V
3A
Open Circuit Protection
360V
Input Protection
Output Protection
© 2011-2012 Microchip Technology Inc.
100%
—
VIN = 13.5V
VIN = 16V
VIN = 9.4V
VIN = 13.5V
VIN = 16V
VIN = 13.5V
VIN = 13.5V
≤ 150s
VIN = 13.5V
—
—
—
—
—
—
—
DS01372B-page 27
AN1372
FIGURE 28:
IGNITOR OUTPUT VOLTAGE WAVEFORM
Voltage scale: 10kv/div
FIGURE 29:
INPUT CURRENT DURING START-UP PROCESS ON A COLD LAMP
Current scale: 2A/div
DS01372B-page 28
Time scale: 500ns/div
Time scale: 2s/div
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE 30:
OPEN VOLTAGE WAVEFORM AND IGNITION FAILED PROTECTION
Voltage scale: 100V/div
FIGURE 31:
Time scale: 200ms/div, 5ms/div
DC BUS VOLTAGE (SUCCESSFUL IGNITION) OF BREAKOVER POINT
Voltage scale: 100V/div
Time scale: 1s/div, 10ms/div
© 2011-2012 Microchip Technology Inc.
DS01372B-page 29
AN1372
FIGURE 32:
LAMP POWER WAVEFORM OF COLD LAMP
Power scale: 30W/div
FIGURE 33:
LAMP POWER WAVEFORM OF HOT LAMP
Power scale: 30W/div
DS01372B-page 30
Time scale: 2s/div
Time scale: 500ms/div
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE 34:
CURRENT FOR COLD LAMP; ZOOM OF THE TAKE-CURRENT
Current scale: 1A/div
FIGURE 35:
Time scale: 2s/div, 500us/div
CURRENT AND VOLTAGE FOR COLD LAMP; ZOOM OF THE DC WARM-UP
CURRENT
Voltage scale: 100V/div
Current scale: 1A/div
© 2011-2012 Microchip Technology Inc.
Time scale: 2s/div, 10ms/div
DS01372B-page 31
AN1372
FIGURE 36:
CURRENT AND VOLTAGE FOR COLD LAMP; ZOOM OF THE RUN-UP STAGE
Voltage scale: 100V/div
FIGURE 37:
Time scale: 2s/div, 10ms/div
CURRENT AND VOLTAGE FOR COLD LAMP; ZOOM OF THE STEADY STATE
Voltage scale: 100V/div
DS01372B-page 32
Current scale: 1A/div
Current scale: 1A/div
Time scale: 2s/div, 10ms/div
© 2011-2012 Microchip Technology Inc.
AN1372
SUMMARY
The reference design presented in this application note
shows a complete fully digital controlled HID ballast
design with simple circuitry and fast response. The
Microchip dsPIC DSC device used in this reference
design provides all of the necessary features and
peripherals to implement a high-performance HID
ballast. Its 40 MHz DSP engine is fast enough to
implement real-time power loop control. Together with
the on-chip Intelligence power peripheral modules
(High-Speed ADC, Comparator, PWM), different
control loops combined with precise timing control was
easily implemented. Fast and smooth transition
between different loops was also developed. The initial
arc was successfully detected, and the subsequent fast
response was provided to maintain it. In addition,
system diagnose and fault protection can also be
implemented without extra components.
Note:
Future plans for this application note
include the addition of MATLAB modeling
information. Please continue to check the
Microchip web site for updates.
© 2011-2012 Microchip Technology Inc.
DS01372B-page 33
AN1372
APPENDIX A:
SOURCE CODE
Software License Agreement
The software supplied herewith by Microchip Technology Incorporated (the “Company”) is intended and supplied to you, the
Company’s customer, for use solely and exclusively with products manufactured by the Company.
The software is owned by the Company and/or its supplier, and is protected under applicable copyright laws. All rights are reserved.
Any use in violation of the foregoing restrictions may subject the user to criminal sanctions under applicable laws, as well as to civil
liability for the breach of the terms and conditions of this license.
THIS SOFTWARE IS PROVIDED IN AN “AS IS” CONDITION. NO WARRANTIES, WHETHER EXPRESS, IMPLIED OR STATUTORY, INCLUDING, BUT NOT LIMITED TO, IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE APPLY TO THIS SOFTWARE. THE COMPANY SHALL NOT, IN ANY CIRCUMSTANCES, BE LIABLE FOR
SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES, FOR ANY REASON WHATSOEVER.
All of the software covered in this application note is
available as a single WinZip archive file. This archive
can be downloaded from the Microchip corporate Web
site at:
www.microchip.com
APPENDIX B:
REVISION HISTORY
Revision A (March 2011)
This is the initial released version of the document
Revision B (April 2012)
This revision includes the following updates:
• The “Getting Started” section and the Ballast
Schematic (see Figure C-1) were updated to
reflect hardware changes made to the reference
design
• In addition, formatting and text changes were
incorporated throughout the document for
clarification purposes
DS01372B-page 34
© 2011-2012 Microchip Technology Inc.
© 2011-2012 Microchip Technology Inc.
APPENDIX C:
FIGURE C-1:
SCHEMATICS AND BOARD LAYOUT
BALLAST SCHEMATIC
D1
400V
RHR660
C2
C1
FCD7N60
Q1
3.3uF/400V
HO2
C6
0.1n/1000V
R2
150R/2W
R5
499R/1W
C10
R47 20k
OUT1
1n/1000V
VS2
BLM31PG121SH1
FCD7N60
Q4
D4
100n/500V
OUT2
L2
C11
100n/500V
HO1
LO2
FR1M
R50 20k
C14
1n/1000V
C13
1.0n/1000V
FCD7N60
Q2
R48 20k
C5
1n/1000V
L3
C52
0.1n/1000V
C53
BLM31PG121SH1
C12
0.1n/1000V 1.0n/1000V
LO1
FCD7N60
Q3
VS1
C15
1n/1000V
R49 20k
Ilamp+
R10
R330/1W
Fault
R12
R330/1W
13.5V
L1
Battery+
1u
C4
100u/25V
R1
10K
D3
C8
104/25V
15V
Q5
Battery-
C3
10n/100V
1
VCC
2
FDD8896
C7
C47
2:12
D6
15V
47u/25V 104/25V
DS01372B-page 35
100u/25V
C17
104/25V
PWM
R11
10k
1
2
3
4
U1
VDD VDD
Input Out
NC
Out
Gnd Gnd
MCP1407
8
7
6
5
*4
FDB3652
10K
3R3/0.25W
AN1372
R9
13.5V
3
Q6
R3
C16
T1
D5 *
SS14
R4
680R/0.25W
dsPIC® DSC DEVICE SCHEMATIC
AN1372
DS01372B-page 36
FIGURE C-2:
U2
Vlamp
Ilamp
Vin
Voltage limit
Current Protection
MCLP
C44
© 2011-2012 Microchip Technology Inc.
104/25V
2
3
4
5
6
7
10
9
1
C45
105/25V
C28
102/25V
8
19
AN0/CMP1A/RA0
AN1/CMP1B/RA1
AN2/CMP1C/CMP2A/RA2
AN3/CMP1D/CMP2B/RB0
AN4/CMP2C/RB9
AN5/CMP2D/RB10
OSCO/CLKO/RB2
OSCI/CLKIN/RB1
MCLR
TMS/RB11
TCK/RB12
PWM2H/RB13
PWM2L/RB14
PWM1H/RA4
PWM1L/RA3
AVSS
AVDD
PGD2/EMUD2/DACOUT/INT0/RB3
PGC2/EMUC2/EXTREF/RB4
VDD
PGD3/EMUD3/RB8
PGC3/EMUC3/RB15
TDO/RB5
PGD1/EMUD1/TDI/SCL/RB6
PGC1/EMUC1/SDA/RB7
VSS
VSS
VCAP
11
12
13
14
15
16
17
18
PWM
R15
0R
L4
R52 1k
3.3V
DS2
Red
EMUD
EMUC
20
C32
dsPIC33FJ06GS202
FB Control
21
22
23
24
25
26
27
28
104/25V
C33
100uF/6.3V
C26
104/25V
3.3V
C27
104/25V
AN1372
FIGURE C-3:
POWER SUPPLY SCHEMATIC
MCP1703
GND
Vout
C19
C29
U3
Rsc1
L5
0R1/1W
22uH/0.5A
104/25V
FIGURE C-4:
place close to VDD (pin13 of dsPIC)
C46
C18
104/25V 100uF/6.3V
1
13.5V
3.3V
3
Vin
2
R51
104/25V 1k
C21
DS1
C31 105/25v
100u/25V
Green
MOSFET DRIVER SCHEMATIC
4
FB Control
3
3.3k
R21
20k
R20
1k
HO2
CT
VB2
102/25V
SD
2
© 2011-2012 Microchip Technology Inc.
HO1
VB1
13
14
VS2
LO2
R14 22R/0.25W
HO1
C22
RT
C24
5
NPN8050
IC1
VS1
LO1
R17
Q7
VCC
C20
105/25V
COM
R13
7.5k
1
VCC
12
6
9
10
8
7
IRS2435D
2.2u/50V
R16 22R/0.25W
R19 22R/0.25W
C48
C49
2.2u/50V
2.2u/50V
VS1
LO1
HO2
C25
C50
C51
2.2u/50V
2.2u/50V
2.2u/50V
VS2
LO2
R23 22R/0.25W
DS01372B-page 37
AN1372
FIGURE C-5:
DEBUGGER, INPUT VOLTAGE, AND OVERCURRENT SCHEMATICS
Debugger
MCLP
R27
4.7K
3.3V
ICD
C34
VPP
VDD
VSS
DAT
CLO
NC
105/25V
EMUD
EMUC
Header 6H
Input Voltage
13.5V
R29
R32
Vin
20k
1k
2k
R35
C37
104/25V
Overcurrent
R30
Fault
Current Protection
2k
C36
DS01372B-page 38
104/25V
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE C-6:
LAMP VOLTAGE AND LAMP CURRENT SCHEMATICS
Lamp Voltage
400V
R28
R34
C39 103/25V
R37
470k/0.25W
5.1K/0.25W
C41
220p/25V
U5:1
2
R44
100k
R45
1
A
3
100k
8
3.3V
750k/0.25W
Vlamp
MCP6002
C40
220p/25V
4
R26
Voltage limit
3K/0.25W
Lamp Current
R46
R33
R41
Ilamp+
2k
C38
10k
104/25V
6
5
MCP6002
U5:2
7
B
C43
104/25V
3.3V
C42
© 2011-2012 Microchip Technology Inc.
Ilamp
4
R39
10k
8
10k
105/25V
DS01372B-page 39
AN1372
FIGURE C-7:
IGNITER CIRCUIT SCHEMATIC
C1
P1
2
1
R1
1K/3W
OUT1
P2
OUT2
D1
D3
D2
SG
R2
6.8M
R3
6.8M
1
2
600V
Connect to Lamp
T1
C2
330n/630V
R4
6.8M
DS01372B-page 40
Trans
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE C-8:
BALLAST BOARD LAYOUT - TOP LAYER
© 2011-2012 Microchip Technology Inc.
DS01372B-page 41
AN1372
FIGURE C-9:
DS01372B-page 42
BALLAST BOARD LAYOUT - MIDDLE LAYER 1
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE C-10: BALLAST BOARD LAYOUT - MIDDLE LAYER 2
© 2011-2012 Microchip Technology Inc.
DS01372B-page 43
AN1372
FIGURE C-11: BALLAST BOARD LAYOUT - BOTTOM LAYER
DS01372B-page 44
© 2011-2012 Microchip Technology Inc.
AN1372
FIGURE C-12: BALLAST BOARD LAYOUT - TOP SIDE
© 2011-2012 Microchip Technology Inc.
DS01372B-page 45
AN1372
FIGURE C-13: BALLAST BOARD LAYOUT - BOTTOM SIDE
DS01372B-page 46
© 2011-2012 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
•
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights.
Trademarks
The Microchip name and logo, the Microchip logo, dsPIC,
KEELOQ, KEELOQ logo, MPLAB, PIC, PICmicro, PICSTART,
PIC32 logo, rfPIC and UNI/O are registered trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
FilterLab, Hampshire, HI-TECH C, Linear Active Thermistor,
MXDEV, MXLAB, SEEVAL and The Embedded Control
Solutions Company are registered trademarks of Microchip
Technology Incorporated in the U.S.A.
Analog-for-the-Digital Age, Application Maestro, chipKIT,
chipKIT logo, CodeGuard, dsPICDEM, dsPICDEM.net,
dsPICworks, dsSPEAK, ECAN, ECONOMONITOR,
FanSense, HI-TIDE, In-Circuit Serial Programming, ICSP,
Mindi, MiWi, MPASM, MPLAB Certified logo, MPLIB,
MPLINK, mTouch, Omniscient Code Generation, PICC,
PICC-18, PICDEM, PICDEM.net, PICkit, PICtail, REAL ICE,
rfLAB, Select Mode, Total Endurance, TSHARC,
UniWinDriver, WiperLock and ZENA are trademarks of
Microchip Technology Incorporated in the U.S.A. and other
countries.
SQTP is a service mark of Microchip Technology Incorporated
in the U.S.A.
All other trademarks mentioned herein are property of their
respective companies.
© 2011-2012, Microchip Technology Incorporated, Printed in
the U.S.A., All Rights Reserved.
Printed on recycled paper.
ISBN: 978-1-62076-213-4
QUALITY MANAGEMENT SYSTEM CERTIFIED BY DNV == ISO/TS 16949 == © 2011-2012 Microchip Technology Inc.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
DS01372B-page 47
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DS01372B-page 48
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11/29/11
© 2011-2012 Microchip Technology Inc.
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